Effect of high hydrostatic pressure on the steady-state kinetics of tryptic hydrolysis of β-lactoglobulin

摘要

The rate of hydrolysis of β-lactoglobulin (genetic variant B) by trypsin in aqueous solution at pH of 7.6 and ionic strength 0.08 M (NaCl) at 25.0℃ increased with increasing hydrostatic pressure. At constant pressure (ambient, 100, 150 and 250 MPa studied), the initial rate of disappearance of β-lactoglobulin B could be analyzed using Michaelis-Menten kinetics (five initial substrate concentrations ranging from 0.11 to 0.88 mM used at each pressure). The over-all catalytic efficiency (ratio between catalytic constant k_c and Michaelis constant K_m) increased by a factor of 10~3 at 250 MPa compared with ambient pressure. While k_c increased only for pressures up to 100 MPa, corresponding to an initial pressure-melted state (factor of 10~2 up to 100 MPa) with no further increase at higher pressure, K_m continuously decreased up to 250 MPa, corresponding to a binding volume of -37 ml mol~(-1) of β-lactoglobulin to trypsin. Thus, the enhanced digestibility of β-lactoglobulin at elevated pressure is the result of a volume decrease during the association process and a volume decrease during the catalytic step. Pressure treatment of whey concentrates should be considered as an alternative processing technology for reduction of allergenicity of whey products.